Migrate data in a PST/EML/MBOX using LegacyFlo is a two-step process. In the first step, the file is first uploaded to a S3 bucket in Mithi's or your account. In the second step, a request is added to LegacyFlo to migrate data from the file to the destination domain.
The PST/EML/MOX file can be uploaded to S3 using the tool S3 browser to be installed on a desktop in your premises.
S3 Browser is a free client interface for users of the Amazon S3 service. It provides an easy to use GUI to manage your buckets and objects.
You can configure the S3 browser on your machine and create an external bucket to upload email data file.